The invention relates generally to electric-actuated automotive emission control valves, such as exhaust gas recirculation (EGR) valves, and in particular to a solenoid actuator for such emission control valves.
An EGR valve may comprise a solenoid as an electric actuator. The solenoid comprises an electromagnet coil and a stator having an air gap at which magnetic flux acts on an armature. The armature motion is transmitted to a valve member to allow flow through a passageway of the valve. Armature motion is resisted by a return spring that acts on the armature, either directly or via the valve member, to bias the armature to a position that causes the valve member to close the passageway.
A known solenoid-actuated EGR valve comprises a stator having an upper pole piece that is disposed at an upper end of the coil and a lower pole piece at the lower end of the coil. The pole pieces have respective annular walls that fit into the open center of the coil, approaching each other from opposite ends of the coil. The juxtaposed ends of the two walls are spaced apart within the open interior of the coil, and their construction and arrangement define an annular air gap disposed circumferentially around the armature. Electric current in the coil creates magnetic flux that passes from one wall across the air gap to the armature, through the armature, and back across the air gap to the other wall. The flux causes magnetic force to be applied to the armature, and the axial component of that force acts to displace the armature along the centerline of the solenoid. Certain changes in coil current will change the magnetic flux spanning the air gap, and possibly also how that flux acts on the armature. Shaping of the interface between each pole piece and the armature is a factor in achieving a desired relationship of armature displacement to coil current.
In an EGR valve, knowledge of the relationship of armature displacement to coil current is essential to a control strategy that accurately meters exhaust gas into the engine intake system.
Accordingly, improvements in the solenoid that would enable desired response to be achieved are seen to be useful, especially as increasingly strict emission regulations become effective, and smaller amounts of exhaust gas need to be metered with increasing precision.
It would also be desirable to provide a basic solenoid construction that can be adapted by designers to create various models of valves possessing desired functional characteristics conforming to various customer specifications.
It is an object of this invention to provide improvements in solenoid actuators, especially those used in smaller automotive emission control valves such as EGR valves, so that more precise control can be achieved.
One general aspect of the invention relates to an mission control valve for controlling flow of gases with respect to combustion chamber space of an internal combustion engine. The valve comprises a valve body comprising a passageway having an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, a valve element that is selectively positioned to selectively restrict the passage, and a mechanism for selectively positioning the valve element. The mechanism comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux and that comprises a wall spaced radially from the centerline. The stator comprises a pole piece that is cooperatively associated with the armature wall and that comprises an inner wall disposed radially inward of the armature wall and an outer wall disposed radially outward of the armature wall. One portion of the air gap flux is conducted from the outer wall to the armature wall, another portion of the air gap flux is conducted from the inner wall to the armature wall, and at least one of the pole piece walls has a radial thickness that changes as a function of its location along the centerline.
Another aspect relates to an emission control valve for controlling flow of gases with respect to combustion chamber space of an internal combustion engine. The valve comprises a valve body comprising a passageway having an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, a valve element that is selectively positioned to selectively restrict the passage, and a mechanism for selectively positioning the valve element. The mechanism comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux and that comprises an annular wall spaced radially from the centerline. The stator comprises a pole piece that is cooperatively associated with the armature wall and that comprises a channel that is annular about, and concentric with, the centerline and that, in radial cross section, has an open throat that faces the armature and is arranged to allow an end portion of the annular wall of the armature to be disposed within the channel for certain displacements of the armature along the centerline.
A further aspect of the invention relates to a solenoid actuator that comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux and that comprises a wall spaced radially from the centerline. The stator comprises a pole piece that is cooperatively associated with the armature wall and that comprises an inner wall disposed radially inward of the armature wall and an outer wall disposed radially outward of the armature wall. One portion of the air gap flux is conducted from the outer wall to the armature wall, another portion of the air gap flux is conducted from the inner wall to the armature wall, and at least one of the pole piece walls has a radial thickness that changes as a function of its location along the centerline.
A still further aspect relates to a solenoid actuator that comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux and that comprises an annular wall spaced radially from the centerline. The stator comprises a pole piece that is cooperatively associated with the armature wall and that comprises a channel that is annular about, and concentric with, the centerline and that, in radial cross section, has an open throat that faces the armature and is arranged to allow an end portion of the annular wall of the armature to be disposed within the channel for certain displacements of the armature along the centerline.
The accompanying drawings, which are incorporated herein and constitute part of this specification, include one or more presently preferred embodiments of the invention, and together with a general description given above and a detailed description given below, serve to disclose principles of the invention in accordance with a best mode contemplated for carrying out the invention.